Experimental investigation of flame pattern transitions in a heated radial micro-channel

Flame pattern transitions of CH4/air mixture were experimentally investigated in a radial micro-channel. These transitions were triggered by a variation in the mixture equivalence ratio or inlet mixture velocity. The transition processes were recorded with a high-speed digital video camera. From the movies, it is shown that the mechanisms responsible for these transitions could be classified into two: (1) transitions from a stable circular flame to a traveling flame, and from a traveling flame to single or double Pelton-like flames were due to local extinction in the flame front, and (2) transition from an unstable circular flame to a spiral-like flame was due to local splitting of the flame front. Numerical simulation of the isothermal flow demonstrated that flow field is symmetric and steady when the inlet velocity is small, but it grows asymmetric and unstable at large inlet velocities. The asymmetric and unstable flow field is expected to be the possible reason for the local splitting of flame front. On the other hand, flame is noted to be quenched near the top wall surface. These two reasons are expected to induce the transition from an unstable flame to a rotating spiral-like flame.

► Flame pattern transitions were experimentally investigated in a micro-channel.
► Transitions were triggered by a change of equivalence ratio or inlet velocity.
► Transitions were due to local extinction or local splitting of flame front.
► Numerical simulation of the isothermal flow demonstrated unstable flow field.